The present invention relates generally to actuator assemblies, and more particularly to actuator assemblies for use with latches in vehicle doors and other closures.
A known vehicle door latch actuator assembly includes an actuator in the form of an electric motor that moves components of a latch from a neutral position to a locked position and an unlocked position.
After the electric motor has moved the latch to the locked position or the unlocked position, the electric motor is powered in the opposite direction to return to the neutral position. When the latch is manually locked or unlocked by, for example, using a key or a sill button, it is not necessary to manually drive the electric motor back to the neutral position, reducing the effort required.
Known vehicle door latch actuator assemblies include a return mechanism employing a helical spring, as shown in European Patent Application EP0267423.
As the electric motor drives in one direction, one end of the helical spring rotates about a longitudinal axis relative to the other end, leaving the helical spring in a torsionally loaded state. When power to the electric motor stops, the helical spring torsionally unwinds to bias the electric motor back towards the neutral position. Therefore, the electric motor does not need to be driven in the opposite direction.
In its simplest form, a helical spring is a spring that is formed by winding wire into a helix along a curved outer surface of an imaginary cylinder. A base of the imaginary cylinder forms a radial plane that, at one end of the spring, lies at 90 degrees to the central elongate (longitudinal) axis of the spring. A coil of the spring is a loop of wire that completes a 360 degree circumnavigation of the imaginary cylinder, and no two points along any given coil exist in any single plane that lies parallel to the radial plane. FIG. 14 of U.S. Pat. No. 4,779,912 shows an example of a helical spring. The elongate axis may also be curved, i.e., where the spring is wound on part of an imaginary torus rather than being wound on an imaginary cylinder.
Further, helical springs are to be distinguished from conical springs, which are distinct from helical springs in that they are formed by winding wire into a helix along the outer curved surface of a cone. FIG. 3 of U.S. Pat. No. 4,821,521 shows an example of a conical spring. Typically, helical and conical springs are used to provide either a compressive force or a tensile force, in other words, to act in an axial manner. However, it is also possible to employ each of these types of spring to provide a torsional bias.
It will be appreciated that helical springs and conical springs are distinct from spiral springs, which will be described in further detail shortly.
A problem with known return mechanisms including helical springs is that, when loaded, there is a tendency for the stress to concentrate in one area of the helical spring, thereby reducing the fatigue life and possibly resulting in the failure of the return mechanism.
The present invention provides an actuator assembly with an increased fatigue life.